A typical radar level gauge described above includes a transmitter receiver circuit board accommodated in a housing and having transmitter receiver circuitry mounted thereon, and an antenna unit extending vertically into a container, in which a measurement object is contained, in order to determine a level of a object by transmit electromagnetic signals and receive the reflected signals. For connecting the transmitter receiver circuit board and the antenna unit with one another, a connection arrangement is required.
A conventional connection arrangement for this purpose is known from Patent Document No. 1 listed below. This document describes a radar level gauge having a transmitter receiver circuit board so accommodated in a housing as to extend horizontally, a probe (or antenna unit), and a connector for connecting the housing and the probe with one another. The connector includes a central conductor, which has one end adapted for insertion into a hole formed in the transmitter receiver circuit board for a direct electrical contact with the circuit board, and the other end adapted for an electrical connection with the probe.
Since the radar level gauge of Patent Document No. 1 has the transmitter receiver circuit board so disposed as to extend horizontally, the level gauge disadvantageously occupies a relatively large horizontal area when mounted in position and it is difficult to minimize the horizontal size of the level gauge. It is, however, often required to mount a radar level gauge and some other devices side by side in the horizontal direction, close to each other, so that it is highly desired to minimize the horizontal size of radar level gauges. In addition, with this known radar level gauge, the position of the hole formed in the transmitter receiver circuit board for receiving one end of the central conductor is limited to be adjacent to the center of the circuit board, which disadvantageously leads to limited freedom in designing the transmitter receiver circuit board.
Patent Document No. 1 also shows another known radar level gauge, which is prior art to the above mentioned radar level gauge (See, FIG. 1 of the document). The prior art radar level gauge has a transmitter receiver circuit board so accommodated in a housing as to extend vertically, and a length of coaxial cable extends out of the circuit board. The tip end of the coaxial cable is adapted for connection with an antenna unit by means of a plug and socket connector pair. Patent Document No. 2 listed below describes a plug and socket connector pair suitable for this purpose. The plug and socket connector pair includes a plug to be connected to the tip end of the coaxial cable extending out of the transmitter receiver circuit board and a socket to be connected to a tip end of a coaxial line leading to the antenna unit. When the plug is inserted in the socket, an inner conductor of the plug and an inner conductor of the socket are brought into contact with each another while an outer conductor of the plug and an outer conductor of the socket are brought into capacitive coupling by means of a dielectric body, so that the transmitter receiver circuit board and the antenna unit are connected with one another while electrical isolation is provided between the ground of the transmitter receiver circuitry and the ground of the antenna.
Since the prior art radar level gauge shown in Patent Document No. 2 has the transmitter receiver circuit board so disposed as to extend vertically, the horizontal size of the radar level gauge may be minimized with ease. On the other hand, however, the use of the coaxial line disadvantageously tends to lead to relatively large transmission losses. In addition, the use of the coaxial line also disadvantageously tends to cause reflection of electromagnetic signals at the connection point (or the feed point) between the coaxial line and the antenna unit.